KMP算法

 1 void Solution::KMPSearch(string pat, string txt)
 2 {
 3     int M = pat.length();
 4     int N = txt.length();
 5     int lps[M]; // 记录最长的相同的前缀后缀的长度
 6     computeLPSArray(pat, lps);
 7 
 8     int i = 0;
 9     int j = 0;
10     while(i < N)
11     {
12         if(pat[j] == txt[i])
13         {
14             i++;
15             j++;
16         }
17         if(j == M)
18         {
19             cout << "Found pattern at index " << i-j << endl;
20             j = lps[j-1];
21         } else if(i < N && pat[j] != txt[i])
22         {
23             if(j != 0)
24                 j = lps[j-1];
25             else
26                 i++;
27         }
28     }
29 
30 }
31 
32 
33 void Solution::computeLPSArray(string pat, int* lps)
34 {
35     int M = pat.length();
36     int i = 1;
37     int len = 0;
38     lps[0] = 0;
39 
40     while(i < M)
41     {
42         if(pat[i] == pat[len])
43         {
44             len++;
45             lps[i] = len;
46             i++;
47         }
48         else
49         {
50             if(len != 0)
51             {
52                 len = lps[len-1];
53             }
54             else
55             {
56                 lps[i] = 0;
57                 i++;
58             }
59         }
60     }
61 }